1. Field of the Invention
The present invention relates to a conveying apparatus which conveys a sheet in a recording apparatus.
2. Description of the Related Art
With the increasing widespread use of ink jet recording apparatuses in recent years, there has been demand for higher image recording quality and reduced sizes and lower costs of recording apparatuses.
To achieve the reduced size and lower cost of a recording apparatus, it is desirable to carry out only U-turn feed rather than two types of feed, namely, straight conveyance and the U-turn conveyance.
The U-turn conveyance requires a U-shaped conveyance path (hereinafter referred to as “the U-turn path”) for reversing a sheet between a feed roller and an LF roller, i.e., reversing the front and the back of the sheet. However, the diameter of the U-turn path is required to be increased to a certain degree in order to reverse a highly rigid sheet used for high image quality without causing the sheet to buckle or warp.
An increased diameter of the U-turn path causes a sheet to be conveyed along a guide substantially on the outer side of the U-turn path, resulting in a longer distance for conveying the sheet in the U-turn path. However, conveying a small-sized sheet, such as, an L-size sheet having a length of 127 mm, requires that the distance between the feed roller and the LF roller be set to a value smaller than 127 mm. Actually, it is difficult to set the distance between the feed roller and the LF roller to be smaller than 127 mm. For this reason, an intermediate roller is usually provided between the two rollers in the case where the diameter of the U-turn path is increased.
In a recording apparatus provided with the feed roller, the LF roller and the intermediate roller, there are cases where a sheet is conveyed in a skewed manner when fed from the feed roller to the LF roller through the intermediary of the intermediate roller. Generally, therefore, the skew is corrected by abutting the leading edge of the sheet conveyed from the intermediate roller against a pair of rollers having the LF roller so as to properly straighten the leading edge, with the LF roller being at rest or rotated in the reverse direction (rotated in the opposite direction from the direction for conveying the sheet).
However, the pair of rollers constituted of the intermediate roller and a driven roller, which is paired with the intermediate roller, continues to sandwich the sheet therebetween, so that the skew of the sheet at the position of the intermediate roller is be corrected. This causes a distortion in the sheet held by the pair of rollers having the LF roller and the pair of rollers having the intermediate roller. The distortion in the sheet in turns leads to a difference in the conveying forces applied to both edges in the width direction of the sheet in the conveyance thereafter, thus conveying the sheet in a skewed manner.
As a solution to the problem described above, there are methods for preventing the distortion of a sheet by temporarily moving an intermediate roller away from the sheet, as disclosed in, for example, U.S. Pat. No. 7,533,878.
To correct the skew of the leading edge of the sheet, the sheet is conveyed by the intermediate roller to abut the leading edge of the sheet against the LF roller while holding the LF roller at rest or rotating the LF roller in the reverse direction. To correct the skew of the leading edge of the sheet, it is necessary to continue to convey the sheet by the intermediate roller until both ends in the width direction of the sheet abut against the pair of rollers having the LF roller.
The sheet continues to be conveyed by the intermediate roller whereas the leading edge of the sheet abutted against the pair of rollers having the LF roller cannot move. If, therefore, the sheet has low rigidity, then the sheet curves in the U-turn path between the LF roller and the intermediate roller. In the case of a highly rigid sheet, however, the sheet cannot curve in the U-turn path between the LF roller and the intermediate roller, thus generating a high conveyance resistance against the intermediate roller.
In the case of the construction disclosed in U.S. Pat. No. 7,533,878, the intermediate roller is supported by a swing arm so as to allow the intermediate roller to be moved away from the sheet. However, when the intermediate roller supported by the swing arm adds to the conveyance resistance, a force moment acts to increase the force of the intermediate roller, which force pushes a driven roller paired with the intermediate roller (hereinafter referred to as “the engaging force”). An increased engaging force causes the pair of rollers, namely, the intermediate roller and the driven roller, to firmly sandwich the sheet, making it difficult to convey the sheet by the intermediate roller. Further, if the state in which the sheet is firmly sandwiched by the pair having the intermediate roller continues, then it becomes difficult to correct the distortion of the sheet between the intermediate roller and the LF roller. As a result, there are cases where the skew of the leading edges of the sheet is not successfully corrected.